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Rossa A.,Centro Meteorologico Of Teolo | Haase G.,SMHI | Keil C.,German Aerospace Center | Keil C.,Ludwig Maximilians University of Munich | And 6 more authors.
Atmospheric Science Letters | Year: 2010

The COST-731 Action is focused on uncertainty propagation in hydrometeorological forecasting chains. The goals and activities of the ActionWorking Group 1 can be subdivided by (1) describing and studying the impact of imperfect observations, mostly from radar, (2) exploiting radar data assimilation as a promising avenue for improved short-range precipitation forecasts and (3) high-resolution ensemble forecasting. Activities of Working Group 1 are presented along with their possible significance for hydrological applications. Copyright © 2010 Royal Meteorological Society and Crown Copyright.

Rossa A.M.,Centro Meteorologico Of Teolo | Laudanna Del Guerra F.,Centro Meteorologico Of Teolo | Laudanna Del Guerra F.,University of Bologna | Borga M.,University of Padua | And 3 more authors.
Journal of Hydrology | Year: 2010

This study aims to assess the feasibility of assimilating carefully checked radar rainfall estimates into a numerical weather prediction (NWP) to extend the forecasting lead time for an extreme flash flood. The hydro-meteorological modeling chain includes the convection-permitting NWP model COSMO-2 and a coupled hydrological-hydraulic model. Radar rainfall estimates are assimilated into the NWP model via the latent heat nudging method. The study is focused on 26 September 2007 extreme flash flood which impacted the coastal area of North-eastern Italy around Venice. The hydro-meteorological modeling system is implemented over the 90km2 Dese river basin draining to the Venice Lagoon. The radar rainfall observations are carefully checked for artifacts, including rain-induced signal attenuation, by means of physics-based correction procedures and comparison with a dense network of raingauges. The impact of the radar rainfall estimates in the assimilation cycle of the NWP model is very significant. The main individual organized convective systems are successfully introduced into the model state, both in terms of timing and localization. Also, high-intensity incorrectly localized precipitation is correctly reduced to about the observed levels. On the other hand, the highest rainfall intensities computed after assimilation underestimate the observed values by 20% and 50% at a scale of 20km and 5km, respectively. The positive impact of assimilating radar rainfall estimates is carried over into the free forecast for about 2-5h, depending on when the forecast was started. The positive impact is larger when the main mesoscale convective system is present in the initial conditions. The improvements in the precipitation forecasts are propagated to the river flow simulations, with an extension of the forecasting lead time up to 3h. © 2010 Elsevier B.V.

Rossa A.M.,Centro Meteorologico Of Teolo | Cenzon G.,Centro Meteorologico Of Teolo | Monai M.,Centro Meteorologico Of Teolo
Natural Hazards and Earth System Science | Year: 2010

In this study consideration is given to the potential use of radar-derived quantitative precipitation estimates (QPE) as flash flood guidance in the context of the Italian Civil Protection flood risk management system. The interest in high precipitation intensities and accumulation motivated the case study of the 26 September 2007 event, in which a quasi-stationary mesoscale convective system brought within 3-6 h 40% of the mean annual precipitation to the wider Venice-Mestre area, i.e. 260 mm in Venice-Mestre and 325 mm in closeby Valle Averto. Comparison of the radar-derived QPE in the area with the rain gauge network revealed a good correspondence for warm season rainfall, both for daily accumulations in the longterm (about 2 years) and hourly accumulations for the case under consideration. The long term average radar to gauge ratio is very close to 0 dB with an uncertainty of approximately ±3 dB, i.e. roughly a factor of two, slightly better for higher precipitation intensities. For the hourly accumulations during this very intense event the spread is similar, while the average is slightly positive. The locations of the rainfall accumulation maximum as detected, respectively, by the radar and by the rain gauge network do not coincide. Given the relatively good quality of the precipitation estimation, it is argued that these areas effectively have received even larger rainfall amounts, and that it is worthwhile to further investigate the potential of radar to be used as flash flood guidance. © 2010 Author(s).

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